Color television system



wwo a... DE FOREST COLOR TELEVISION SYSTEM 3 Sheets-Sheet 1 Filed Jan.15, 1945 INVENTOE LEE 5 Foessr .B/ Hana/5,1? cw, Ever-2 &/%wm5 @d. 26,39%. 1.. DE FOREST 3 COLOR TELEVISION SYSTEM Filed Jan. 15, 1945 3Sheets-Sheet 2 sww- Saw/c OSCILLATOR AMPLIFIER 1N vzwroz LEE DE F0225?.W ana/s, lf/zcdfbsrm 6t HARE/5 Quiz. 26, 3948.. L. DE FOREST COLORTELEVISION SYSTEM 3 Sheets-Sheet 3 Filed Jan. 15, 1945 [NVENTDE L5: asFbREsT F02 7745 Hem JQTTO/QNEY? Patented Oct. 26, 1948 UNITED STATESPATENT OFFICE COLOR TELEVISION SYSTEM Lee de Forest, Los 'Angelea,Calif.

Application January 15, 1945, Serial No. 572,863

9 Claims. 1

My invention relates to a new and useful television system fortransmitting, receiving, and projecting in natural colors objectspresented before a television pick-up camera or iconoscope at thetransmitting station.

Heretofore systems for televising objects in their natural colors withany substantial degree of accuracy have usually employed revolving colorsector discs comprising color filter sections of either two or threecolors. In such television systems the color filter disc is located atthe transmitter between the object and the pick-up camera or iconoscopeand at the receiver between the fluorescent screen of the kinescope orcathode beam projection tube and the observer. Such systems require thatthe diameter of the rotating disc be considerably more than twice thediameter of the cathode beam receiving tube. when such tube is largeenough to give a satisfactory picture without projection upon thefluorescent end of the tube, e. g., a picture at least 6" x 8" indimensions, such rotating color disc must be approximately 2 feet indiameter and obviously requires a relatively large synchronous motor,involving excessive power and disturbing noise, for the rotation of thedisc at the required speed.

Furthermore, in such systems which require color filter sectors ofsubstantial dimensions, at least somewhat larger than the dimensions ofthe picture itself upon the end of the kinescope tube,

the picture is completely viewed in color sequence; that is, onecomplete frame is viewed through each of the three color sectors, 1. e.,the red, blue, and green sectors, or one picture field, made up ofalternate lines only, is viewed in succession through each of such threecolor sectors. In either case and in order to avoid the highlyobjectionable color fringes or flicker, particularly when the objectviewed at the transmitter is rapidly moving, it is necessary that thenumber 40 increases, the width of the required video frerate of 30 persecond. Usually such increase required is double the foregoing rate, or60 comquency band for such projection must be correspondingly increased.Thus, where a frequency band of 6 or 6.5 megacycles is consideredadequate for satisfactory projection in present television systemsprojecting 525 line pictures in black and white, a band width of two orthree times the black and white band width is required for three colortelevison transmission employing color sector discs. Such increase inthe frequency band requires that the main or carrier frequency of suchtelevision transmisson be increased from the present standard frequencyregion of 50 to 70 megacycles to several hundred megacycles.

Further, when the carrier frequency is raised to these upper limits, newdifliculties and problems in transmission arise, such as overcoming thegreatly diminished efficiency of the transmitting tube at suchfrequencies, the substantial increase in the number of shadow castingobstacles, and .the increased number of ghost images presented by thehigher reflectivity of objects to the higher carrier frequencies.

Among the objects of my invention is the provision of a system oftransmitting and projecting television pictures in natural colors whichavoids such difliculties and problems, which eliminates the necessityfor an increase in the number of pictures transmitted per second, andwhich employs the portion of the frequency spectrum now employed for thetransmission of black and white television pictures with its numerousand great advantages.

Embodiments of my invention are described in the followingspecification, which may be more readily understood by reference to theaccompanying drawings. In the drawings Fig. 1 is a vertical sectionalview of a pick-up camera, or iconoscope tube employed as a part of thetelevision system of my invention;

Fig. 2 is a horizontal sectional 'view of the apparatus illustrated inFig. 1:

Fig. 3 is a side elevational view of the appaplete picture scans persecond, and such an inratus illustrated in Fig. 1;

crease in.pictures makes necessary a corresponding increase in the speedof rotation of the color sector discs at the transmitter and receiver.

It will be seen, therefore, that the present television systems fortransmitting and receiving images in natural colors, and including suchrotating color sector discs, involve substantial obstacles andobjections preventing or impairing their public acceptance.

Furthermore, as is well recognized, as the num- Fig. 4 is an enlargedfragmentary plan view of the light-transparent curtain used with theapparatus illustrated in Figs. 1 to 3, inclusive;

Fig. 5 is an enlarged fragmentary sectional view of the curtainillustrated in Fig. 4;

Fig. is a side elevational view, partially sectioned, of thekinescopetube and the remainder of the synchronizing apparatus for thesynchronizing of the curtains in accordance with my invention;

Fig. 8 is a fragmentary plan view of the end of the kinescope tubeillustrated in Fig. 7;

Fig. 9 is a vertical sectional view, partially diagrammatic, of theapparatus illustrated in Fig. '7;

Fig. 10 is a side elevational view, partially sectioned, of a modifiedform of apparatus of my invention;

Fig. 11 is a diagrammatic view illustrating the relationship between thecolored stripes upon the light-transparent curtain and the sweeps of thecathode beam; and

Fig. 12 is a diagrammatic view illustrating the relationship between thecolor stripes upon the transparent curtain and the cathode beam sweepwhen the stripes are horizontally disposed and the curtain is movedvertically.

With reference to the drawings, which are for illustrative purposesonly, the numeral 2| indicates a pick-up camera or iconoscope or cathodebeam'tube of conventional construction, and including an enlargedportion 22 and an elongated cated by the numeral 21 and are brought outof the tube through the end of the elongated cylindrical portion 23.

The enlarged portion 22 of the cathode beam tube is enclosed within orsurrounded by an endless band, screen, or curtain 28. The curtain 28isosupported upon rollers 29, 30, 3i, and 32 suitably mounted forrotation, is held taut by a teni sion spring 33 connecting the roller 32to a suitable base, and is maintained in firm contact with the roller31, which is the driving roller, by idle rollers 34 and 35. The drivingroller 3| is driven by an electric motor 36 through a geared connection31 with its shaft I8 at a speed which may be very low, as, for example,of the order of 9 to 13 inches per minute of linear movement of thecurtain 28. If desired for any reason, the speed of movement of thecurtain as may be made much greater than this order, there being nodefinite relationship between thespeed of travel of the curtain and thatof the cathode beam sweep or the number of sweeps per second of thecathode beam across the mosaic plate 24. The broken line indicated bythe numeral a indicates an object, light rays from which are passedthrough a collecting lens 40 and a colllmating lens' 4| in a housing 42,so that the light rays passing from the lens 4| to the mosaic plate 24are parallel.

The curtain 28 is light-transparent and provided over its entire surfacewith contiguous, narrow vertical stripes 43. These stripes are in groupsof three colors, red, blue, and green, as indicated by the letters R, G,and B in Fig. 4, the exact shades of such colors being so selected that,when viewed in rapid motion, the impression of white is conveyed to theretina of the eye, 1. e.. the

combination of shades of the three colors coiliprises the entirespectrum visible to the human eye.

The width of each individual stripe is determined by the diameter of thearea of the mosaic plate 24 impinged upon by the cathode beam at anyposition of its travel; for example, if the dimeter of the cathode beamat its impingement upon the mosaic plate 24 is .002 inch, the width ofeach individual stripe 43 upon the curtain 28 is equal to at least .002inch and may be somewhat greater. 1,

The curtain 28 is preferably constructed of flexible material, such ascellophane, celluloid, or

thin white silk made transparent. as by impreg-.

nation with a suitable glazing material. To provide additionalmechanical strength I prefer to provide to each edge of the curtain 28 areinforcement or hem 44 formed of linen or thin flexible material, suchas steel or bronze. The lower hem 44 is provided with a plurality ofperforations 45 which may be of any desired form and are 11-. lustratedas substantially square in the drawings. These perforations 45 serve totransmit light through the hem 44 which is opaque in order tosynchronize the movement of the curtain 24 with the movement of asimilar curtain at the receiving station utilizing apparatus illustratedin Fig. 6.

The numeral 48 indicates a lamp so positioned with respect to areflector "that light rays from the lamp 46 are directed through a lens48 and one of the perforations 45 when it is directly aligned with thelamp 4i, reflector 41, and lens 48. A photoelectric cell 49 ispositioned upon the opposite side of the hem 44 and so shielded thatlight can fall upon the cathode electrode thereof only when it istransmitted through one of the perforations 48 and a collector lens 50.When a flash of light is thus passed through one of the delivered to thegenerator of the audio-carrier high frequency and is radiated therefromin the form of a pulse of supersonic frequency to be picked up by thereceiving antenna. The circults involved in the amplifier II andsupersonic oscillator 52. being well known to those skilled in the art,are not illustrated or described in detall, nor for the same reason isthe ampllfler or filter circuit at the receiving station by which thissupersonic pulse is received. v

The received supersonic pulse is detected and amplified by an amplifier53 and led to a thyratron tube 54, the output of which is connected to agaseous glow or flash lamp 5!. The lamp II is so positioned with respectto a reflector N and a 7 lens 51 that light from the lamp is isprojected through one of the perforations 45a in a curtain 28a,identical with the curtain 28 previously described, when suchperforation is in alignment with the lamp '5, reflector 5i, and lens 51.

' All of the light from the lamp 55 which passes through one of theperforations 45a, when it is in advance of its proper position with respct to the curtain 28 at the transmitter, light from the lamp 88, when itis flashed, passes through one of the perforations 48a and enters thetransparent wedge 88 and is conducted therefrom to a photoelectric cell8|. Similarly, if the curtain 28a at the receiver is slightly behind itsproper position to be synchronized with the curtain 28 at thetransmitter, when the lamp 55 is flashed, light passes therefrom throughone of the perforations 45c and falls upon the transparent wedge 88 andis conducted therefrom to a photoelectric cell 82.

The output of cells 8| and 82 is connected through amplifiers 88 and 84,respectively, to a supersonic oscillator 88 having a circuit arrangementwell known in the art, such that its output responsive to the amplifiedimpulse from cell 8| is of one supersonic frequency, for example I!kilocycles, while its output responsive to the amplified impulse fromthe cell 82 is a different supersonic frequency, for example 20kilocycles.

These amplified supersonic impulses of and kilocycles are filtered outthrough appropriate fllter circuits, well known in the art and hence notdescribed in detail, and the resultant pulses are detected and amplifiedthrough amplifiers 88 and 81. The rectified output of the amplifiers 88and 81 is led to the coils of two relays 88 and 88, respectively, theoperation of which is described hereinafter.

The numeral In in Fig. '7 indicates an iconoscope or cathode beam tubeat the receiving station. The cathode beam tube I8 is of conventionalconstruction and includes a cathode beam gun II and deflecting plate I2for causing the cathode beam to scan a fluorescent picture area II toprovide an illuminated image of the object 88 at the transmitter.

The curtain 28a is arranged immediately adjacent the fluorescent picturearea I8, and on the opposite side of the curtain 280. a reflector 14 ispositioned at an angle of substantially with the plane of the picturearea It to project the light therefrom vertically upon a second inclinedreflector I8. The second reflector I5 is so positioned as to reflect thelight against a viewing screen I8 from the reflector I4 substantiallyparallel to the light rays directed from the picture area I8 against thereflector I4. The picture may be viewed either from the front or rear ofthe viewing screen I6, according to the type of viewing screen employed.

It would, of course, 'be possible to pass the color curtain 28acompletely around the cathode beam tube 18 in the manner that it passesaround the smaller cathode beam tube 2! at the transmitter. However, thereflector arrangement described avoids such an inconveniently greatlength for the curtain 28a by permitting this curtain to pass aroundonly the reflector 14. In such travel the curtain 28a is supported byrollers 'I'l similar to the rollers supporting the curtain 28 andpreviously described.

In the apparatus previously described it is desireable that the curtain28a pass very close to the picture area I8 in order to avoid colorconfusion resulting from diflusion of the light rays from variouselements of the picture image through stripes 43 other than the stripesof the appropriate color. In the apparatus as illustrated this colorconfusion is avoided by positioning the curtain 28a practically incontact with the flattened surface of the cathode beam tube 18 uponwhich the picture area I8 is located. If the curtain 28a 6 is spacedsome distance from the picture area 18, the color confusion referred tomay be avoided by the use of an optical projection system locatedbetween the picture area I8 and the curtain 28a as is hereinafterdescribed.

As best illustrated in Fig. 'I, 'the cathode beam tube I8 is mountedupon a fiat support I8 pivoted at its rearward end on a, pin I8supported upon a base 88. The tube I8 is supported upon this support I8by clamps 8| which extend around a portion of the periphery of the tube.At its forward end the support I8 rests upon two rollers 82 mounted uponan upright 88 attached to the base 88. Adapted for rolling contact withthe cesses 88 and 81 provided in the tops of armature members 88 and 88,respectively. As illustrated in Fig. 9, the recesses 88 and 81 areprovided with downwardly converging bottom walls.

. It will be seen that, when the armature member 88 is attracted bycurrent passing through the relay coil 88, th ball 88 is forced intoclose'and propelling contact with the support |8 so as to propel thesupport I8 toward the right. Likewise, when the armature member 88 isattracted by current passing through the relay coil 68, the ball 88 isforced into driving contact with the support 18 so that the support I8with the cathode beam tube 18 is moved to the left.

When one of the balls 84 or 85 is in propelling contact with the supportI8, the other of such balls is disengaged from the support I8 so thatthe support is free to move either to the right or to the left inresponse to contact with one ball or the other. By this arrangement thecathode beam tube 18 is shifted slightly to the right or left so thatthe vertical color stripes 48 in the curtain 28a will register perfectlywith the corresponding color stripes in the curtain 28 at thetransmitter.

Where both the transmitter and the receiver are operated from the samepower network, there is only a practically negligible tendency on thepart of the curtains 28 and 28a to become displaced from each other.even by the width of half of a single stripe 43, so that no automaticsynchronizing device is necessary under such circumstances. Suchadjustment as is required for such an arrangement may be effected by anadjusting screw 88 threaded through an upright 8| of the base 88 andengaging one side or the support II and a spring 82 resiliently engagingthe other side of the support I8 and an upright 88 secured to the base88. The adjusting screw 88 is not employed if the automaticsynchronizing apparatus herein described is used.

It is in any event necessary that the lateral location of the cathodebeam picture upon the picture area I8 of the cathode beam tube I8 be atall times positive and exact. However with the existing methodsof linesweep synchronization the dimensions and location of the cathode beampicture are maintained with extreme accuracy.

Illustrated in Fig. 10 is a modified form of apparatus in which thecurtain 28a is spaced from the picture area I3 and the flattened end ofthe cathode beam tube 18. In this apparatus lenses 88 and 88 areprovided in a housing 91a in position to collect the rays of light fromthe picture area I8 and to transmit them as horizontal rays through thecurtain 28a in close proximity to the lens 88 and against an inclinedreflector 81. The reflector 8I reflects these rays against a secondreflector 88, which in turn reflects the rays'in a directionsubstantially parallel to the rays which pass from the picture area I2through the lens 88. The curtain 28a is looped around the reflector 81and may be supported and driven in the manner previously described.

In the apparatus illustrated in Fig. the synchronization of the stripesof corresponding color in the curtain 28:: at the receiver and thecurtain 28 at the transmitter are accomplished with the same apparatusas that described in connection 10 with Figs. 7, 8 and 9 by moving thelens housing 81:: parallel to th direction of movement of the curtain28a.

Referring to Fig. 11, if it be assumed that light rays from a small blueobject pass through the area indicated by the numeral I88 upon thecurtain 28 in front of the cathode beam tube 2 i, and that such area isincluded within one of the stripes 42 which is red, the light rays fromthis blue object will not be transmitted through the curtain 28 for /30of a second. This is for the reason that, if the curtain is travellingfrom right to left, and the next adjacent stripe 43 is green, the secqndsweep of the cathode beam will be on the line indicated by the numeral 2in Fig. 11 rather than upon the line indicated by the numeral I. Whenthe cathode beam again arrives at the sweep indicated by the numeral I,a stripe 48 of blue color on the curtain 28 will be interposed betweenthe rays of light from such 30 blue object, and such rays will thereforebe transmitted to the spot on the mosaic plate 24 corresponding to thearea Hill.

The shift of the curtain 28 from .the first red stripe to the secondblue stripe will represent /30 of a second. if, on the other hand, agreen object were presented to the area indicated by. the numeral Hi8,instead of a blue object, /is of a second would elapse before a stripe48 on the curtain which is green will be in position to trans- 4o mitthe rays of green light upon the area of the mosaic plate 24corresponding to the area indicated by the numeral I80.

Therefore, it will be seen that any color spot of the image is delayednot longer than /15 of a second for a stripe 42 on the curtain 28 ofcorresponding color to appear before it and thus permit light rays fromsuch color spot to pass through the curtain 28 to the mosaic plate 24.

-As the horizontally travelling cathode beam 50 scans the picture fromleft to right and from top to bottom, unless the object 38 before theoathode beam tube 2| is moving with extreme rapidity, every individualelement or section of the object optically projected upon the curtain 28will find a stripe 48 of corresponding color on the curtain 28 for thetransmission of its proper 'color to the mosaic plate 24 of the cathodebeam screen 18, the rapid horizontal interlaced sweep of the cathodebeam across the curtain 28 upon the face of the mosaic plate 24 and thevery slow and transverse movement of the current 28 providing a'varl-colored projected image in which extremely small properly coloredelements appear all over the face of the mosaic plate 24. These properlycolored elements upon the mosaic plate 24 are, as will be apparent fromthe foregoing, reproduced with the same fidelity upon the viewing screen18.

Instead of employing curtains 28 and 28a with stripes .43 extendingvertically, I may employ a curtain of the same character with thestripes of color extending horizontally, the arrangements of mirrors,lenses, and drive means being the same as described in connection withthe curtains 28 and 2842 except that they are rotated through Thehorizontal arrangement of stripes 48, however, is not as satisfactory asthe vertical arrangement. I

This is illustrated in Fig. 12, where I hav shown a cross section of avertically moving our.- tain 28b having stripes 43b extendinghorizontally. These stripes 42b are like the stripes 42, previo lfl ydescribed, as to color and sequence.

In the column headed C there is illustrated the successive sweeps of thehorizontally moving cathode beam of the cathode beam tube 2|, assumingfor the purpose of simplification that the beam scans successive linesand not alternate lines as in actual practice. In the column headed D Ihave shown the relative positions of the successive sweeps oi thecathode beam and the curtain 28b when the curtain has moved upwardly adistance equal to half of the diameter of the cathode beam'at itsimpingement upon the mmsaic plate 24. K

With the relative positions of the cathode beam sweeps in the column Dand the stripes 4812, it will be evident that the cathode beam sweepingpath i is travelling along both a red and a blue horizontal stripe. Thisresults in the projection upon the mosaic plate 24 of a section of theobiect 29 through half a red stripe and half .a

blue stripe 42b. giving the sensation of purple upon the retina of theobserver's eye, thus incorrectly presenting the true color of thecorresponding section of the object.

Thus, if the corresponding section of the oblect were red and thescanning beam of the oathode beam tube 2l were astride a red and bluestripe 42b of the curtain 28b, the resultant electron impulse from thecathode beam tubeli will be that resulting from the red lighttransmitted to the curtain 28b, being only half transmitted through thecurtain 28b. Therefore, at the receiving cathode beam tube 18 theintensity of the scanning beam at that section of the image will bereduced by half, and this reduced illumination will be divided betweenthe red and blue stripes, resulting in a dim purple colored section ofthe image, instead of a bright red colored sec tion.

The diminution of light intensity at this instant in such a' smallsection might be overlooked, because within /30 or not to exceed /15 ofa second thereafter or less a succeeding red stripe 43b of the curtain28b would be in proper position to give the proper eye sensation ofcolor and the proper intensity of illumination. However, as hereinbeforestated, there would be a sensation of purple projected along the entiresweep of the cathode beam represented by the path i, if it be assumedthat a horizontal red stripe existed on the object 38 at the area beingscanned, so that the integrated sensation of the eye would be a blendingof a red line followed by a purple line giving distorted color sensationfor that section of the object.

.It will thus be apparent that color errors or distortions are involvedin the use of a curtain 9,. with horizontal stripes of color which donot occur when the curtain is provided with vertical color stripes.

The disadvantage of a curtain with the horizontal stripes may be reducedor eliminated by moving the curtain 28b vertically step-by-step withsufiicient suddenness rather than by slow continuous motion. In such amanner the paths of the beam sweep indicated by the numeral I, forexample, coincides successively with stripes 43 of red, blue, and greencolor. In such a manner there may be secured an effect in generalsimilar to that obtained by the conventional three-color rotating filterdisc, except that the colors of the projected image will be intermingledduring any single scanning. Such intermingling will result in far lesscolor fringing and flicker than in the use of the conventional rotatingcolor disc, and likewise provides the extremely important advantage ofproviding color images at a scanning rate of thirty pictures .per secondequal in excellence to those obtained with the conventional rotatingcolor disc and a scanning rate two or three times this figure.

However, such intermittent motion of the cur tain 28b with the stripes43b extending horizontally presents mechanical difficulties in view ofthe frequency with which such motion must occur.

It will be obvious that, instead of employing stripes 43 or 43b upon thecurtains 28. 28a. and 28b of three colors in sequence, as hereinbeioredescribed, I may employ stripes in two-color se quences, thus permittingan even slower movement of the continuously or intermittently propelledcurtains. However, it is well known that the reproduction of naturalcolors by the use of a two-color process or apparatus is onlyapproximately perfect and not entirely satisfactory, and I thereforeprefer to employ the three colors in sequence to cause the projectedimage to truly present the natural colors of the object.

The numerous advantages of my invention hereinbefore described are notrestricted to a television scanning system employing 525 or any precisenumber of lines to a picture and or any precise number of completeframes, or 60 or any precise number of scanning fields per second.

The advantages of my invention hereinbefore described are enhanced ifthe number of lines of the picture be substantially increased.Obviously, if the number of lines to the picture be increased, the widthof the stripes 43 and 43b should be proportionately reduced. It is notnecessary for the reasons set forth to increase the number of picturescans per second in order -to obtain satisfactory reproduction of theimage in correct natural colors. It will be apparent that variousmechanical arrangements and devices other than those I have illustratedand described may be employed to efiect the modes of operation and theresults of the mechanical arrangements and constructions I haveillustrated and described for illustrative purposes. Such arrangementsand many variations and modifications of the apparatus illustrated anddescribed will readily occur to those skilled in the art to which theinvention is related, and my invention should therefore be understood asnot restricted to the specific embodiments illustrated and described butas including all arrangements, modifications, and additions comingwithin the scope of the claims which follow.

I claim as my invention:

1. In a color television system wh ch includes a 10 cathode beam tubehaving means for generating a cathode beam and having means for movingthe beam along parallel paths, the combination of: a movable filterdisposed adjacent the cathode beam tube, said filter comprising aplurality of sequentially arranged stripes of different colors, saidstripes being perpendicular to the direction of movement of the cathodebeam; and means for moving said filter at a uniform speed in a directionperpendicular to said stripe 2. Ina color television system including apair of cathod beam tubes one of which is associated with a transmitterand the other of which is associated with a receiver, the cathode beamtube at the receiver being movable, the combination of: a firstmulti-color filter disposed adjacent the cathode beam tube at thetransmitter and provided with a plurality of perforations therethrough;first light-producing means adapted for directing light rays through oneof said perfora tions through said first multi-color filter; firstlight-responsive mean-s in the path of said light rays from said firstlight-producing means; means for moving said first multi-color filter; asecond multi-color filter disposed adjacent the cathode beam tube at thereceiver and provided with a plurality of perforations therethrough;second light-producing means adapted for directing light rays throughone of said perforations through said second multi-color' filterwhenever light rays from said first light-producing means fall on saidfirst light-responsive means; second light-responsive means in the pathof light rays from said second light-producing means; means for movingsaid second multi-color filter; and

means actuable by said second light-responsive means for moving thecathode beam tube at the receiver whenever light rays from said secondlight-producing means fall on said second lightresponsive means.

3. In a color television system which includes a tube having means forgenerating an electron stream, means for causing said electron stream toscan a field in said tube in a plurality of parallel paths and meansproviding a light path for said field, a movable light filter disposedin said light path, said filter having a plurality of sequentiallyarranged stripes of different colors extending transversely of saidparallel paths, and means for moving said filter at a uniform speed inone direction to move said stripes transversely of themselves across thelight path for said field and at a speed causing the scanning of saidfield to cross a multiplicity of said stripes in each of said parallelpaths.

4. In a color television system which includes a cathode beam tube forgenerating a cathode beam, means for moving the end of the beam to causesaid end to scan a field in said tube in a plurality of parallelpathsand means providing a light path for said field, a movable light filterdisposed adjacent said cathode beam tube and in said light path, saidfilter having a plurality of sequentially arranged stripes of differentcolors extending transversely of said parallel paths, and means formoving said filter at a uniform speed in one direction to move saidstripes transversely of themselves across the light path for said fieldand at a speed causing said end of said beam to cross a multiplicity ofsaid stripes while moving along each of said parallel paths.

5. In a color television system which includes a tube having means forgenerating an electron stream, means for causing said electron stream toscan a field in said tube in a plurality of parll allel paths and meansproviding a light P th for said field, a movable light filter disposedin said light path, said filter having a plurality of sequentiallyarranged stripes of difierent colors extending transversely of saidparallel paths, and means for moving said filter at a uniform speed inone direction to move said stripes transversely of themselves across thelight path for said field and at a speed causingthe scanning ofsaidfield to cross a multiplicity of said stripes in each of saidparallel paths, said tube having an image receiving surface constitutingsaid field scanned by said electron stream, said filter being positionedclosely adjacent and substantially parallel to said surface.

6. In a color television system which includes a tube having means forgenerating an electron stream, means for causing said electron stream toscan a field in said tube in a plurality of parallel paths and meansproviding a light path for said field, a movable light filter disposedin said light path, said filter having a plurality of sequentiallyarranged stripes of diil'erent colors extending transversely of saidparallel paths, and means-for moving said filter at a uniform speed inone direction to move said stripes transversely of themselves across thelight path for said field and at a speed causing the scanning of saidfield to cross amultiplicity of said stripes in each of said parallelpaths, said filter being an endless fiexible curtain extending aroundsaid tube.

7. m a color television system which includes a tube having means forgenerating an electron stream, means for causingsaid electron stream toscan a field in said tube in a plurality of parallel paths and meansproviding a light path for said field, a movable light filter disposedin said light path, said filter having a plurality of sequentiallyarranged stripes of different colors extending transversely of saidparallel paths, and means for moving said filter at a uniform speed inone direction to move said stripes transversely of themselves across thelight path for said field and at a speed causing the scanning of saidfield to cross a multiplicity of said stripes in each of said parallelpaths, said filter being an endless flexible curtain forming a closedloop with a portion of said curtain adjacent said tube and a portionremote from said tube and an angularly positioned mirror within saidloop to cause said light path to pass through said adiacent portion onlyof said curtain.

8. In a color television receiver which includes. a cathode beam tubefor generating a cathode beam, means-for moving the end of the beam tocause said end to scan a field in saidwtube in a plurality of parallelpaths and means providing a light path for said field, a movable lightfilter disposed adjacent said cathode beam tube and said light path,said filter having a plurality of sequentially arranged stripes ofdifferent colors extending transversely of said parallel paths, meansfor moving said filter at a uniform speed in onedirectionto move saidstripes transversely of themselves across the light path for said as v434,368

assaaos field and at a speed causing said end of said beam to cross amultiplicity of said stripes while moving along each of said parallelpaths, means for receiving and detecting light filter synchronizingpulses. means for converting said synchronizing pulses into light pulsesand directing said light pulses toward said filter, said filter havinglight interrupting and light transmitting portions in the path of saidlight pulses, the position of said portions of said filter beingcorrelated with the position of said stripes and means including aphotoelectric device responsive to light from said lizht pulsestransmitted through said light transmit'ting portions for moving saidfilter and tube relative to each other in a direction transversely ofsaid stripes to maintain color synchronization of said receiver.

9. In a color television receiver which includes, a cathode beam tubefor generating a cathode beam, means for moving the end 01' the beam tocause said end to scan a field in said tube in a plurality of parallelpaths and means providing a light path for said field, a movable lightfilter disposed adjacent said cathode beam tube and said light path,said filter having a plurality of sequentially arranged stripes ofdifi'erent colors extending transversely of said parallel paths, meansfor moving said filter at a uniform speed in one direction to move saidstripes transversely of themselves across the light path for said fieldand at a speed causing said end of said beam to-cross a multiplicity ofsaid stripes while moving along each of said parallel paths, means forreceiving and detecting light filter synchronizing pulses, means forconverting said synchronizing pulses into light pulses and directingsaid light pulses toward said filter, said filter having lightinterrupting and light transmitting portions in the path of said lightpulses, the position of said 0 portions of said filter being correlatedwith the receiver.

LEE l: FOREST.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,130,221 ,Van Riper Mar. 2, 19152,310,863 ,Leverenz Feb. 9, 1943 2,317,989 Goldmark May 4, 19432,319,803 Dyer May 25, 1943 2,319,805 Dyer May 25, 1943 2,389,979I-Iufi'nagle Nov. 27, 1945 FOREIGN PATENTS Number Country Date GreatBritain Sept. 9, 1995

